JEE Main 202624 JanuaryMorning Shift
- Exam
- JEE Main
- Year
- 2026
- Date
- 24 January
- Shift
- Morning Shift
- Subject
- Chemistry
- Chapter
- Alcohols Phenols and Ethers
JEE Main 2026 · 24 January · Morning Shift · Chemistry · Alcohols Phenols and Ethers
A hydroxy compound (X) with molar mass 122 ~g ~mol^ -1 is...
A hydroxy compound with molar mass is acetylated with acetic anhydride, using a large excess of the reagent ensuring complete acetylation of all hydroxyl groups. The product obtained has a molar mass of . The number of hydroxyl groups present in compound (X) is:
Options
- A5
- B2
- C4
- D3
Correct answer
C. 4
Step-by-step solution
In acetylation, each hydroxyl group reacts:
R-OH + (CH₃CO)₂O → R-O-CO-CH₃ + CH₃COOH.
Each -OH is converted to -OCOCH₃, resulting in a net mass increase of 42 g/mol per hydroxyl group (addition of acetyl group mass 43, removal of hydrogen mass 1).
Given: Original molar mass = 122 g/mol, Product molar mass = 290 g/mol
Total mass increase = 290 - 122 = 168 g/mol
Number of hydroxyl groups = 168 ÷ 42 = 4
R-OH + (CH₃CO)₂O → R-O-CO-CH₃ + CH₃COOH.
Each -OH is converted to -OCOCH₃, resulting in a net mass increase of 42 g/mol per hydroxyl group (addition of acetyl group mass 43, removal of hydrogen mass 1).
Given: Original molar mass = 122 g/mol, Product molar mass = 290 g/mol
Total mass increase = 290 - 122 = 168 g/mol
Number of hydroxyl groups = 168 ÷ 42 = 4